One of those locking "puzzle nuts" or "lock lugs" used to prevent theft of high-priced automotive rims. Typically, one standard lug nut per rim is replaced with a bling nut. Bling nuts can not be easily removed without access to the corresponding specially-keyed socket.
Expensive aftermarket rims are a typical bling
accessory added to cars to customize the appearance.
I used bling nuts and everything but those pricks still managed to jack the rims off my car last night.